Having previously had 3 dogs, now down to 2 - I can tell you that having 2 is no more hassle then having 1.
You still have to do all the things you do for your first dog, so it's no extra 'bind'. They're small enough to fit in the back of the car together (I have a GSD and a Boxer, so if mine can fit, a staffie and EBT should 
)
My main reservation would be how would your staffie take to the other dog - do you think he would enjoy the company of the new dog, or feel pushed out?
Also be prepared that the new dog might have issues and might be harder work than your existing dog, so life might be more difficult for a while, until he settles in.
On the plus side - while my dogs don't really do much together in the house (grumpy GSD can't be bothered with the Boxer loving), they certainly keep each other active when out on walks. My boy is getting older and left alone he would just plod alongside me on walks. With his hyper Boxer sister, he bounces around and has a great time.
If you really can't persuade your DH, could you try sharing this dog's details among your friends to make it your mission to find a home for him? I managed to do this with a friend - they said they were looking for a dog after losing their own, and so I tortured myself looking at adorable dogs on the rescue websites - I wanted them all. I found one particularly gorgeous boy, sent them the details and they adopted him the very next day! Now I get to cuddle him, and know he's in a very happy home, without having to take him on myself.
As an aside - what utter torture to have the dogs at the RSPCA visible to passing people. I wouldn't be able to walk past in case I saw 'the one'.
Good luck persuading your DH, I too think this little dog has chosen you